• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 29 subscribers
  • Views 432 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

DRV10970: PWM input - Duty cycle step size/resolution

DRV10970: The max error and resolution for the PWM speed control commend

Lacey Lin
Intellectual 2900 points
Part Number: DRV10970
Other Parts Discussed in Thread: DRV10974, DRV10866

Hi team,

My customer use the 25kHz PWM to control the speed of motor.

In the previous post, you have mentioned that the resolution of the PWM is about 0.2% for DRV10970.

So I want to know the max error if I input a stable duty cycle PWM signal?(The error between the theory speed and the exactly speed).

Lacey

Thanks a lot!

  • 0
    TI__Expert 6065 points
    Hey Lacey,

    When I read the previous post, it seems like the pwm resolution of 0.2% is referring to DRV10974 and DRV10970 doesn't have that pwm resolution. I can confirm with my team, but I want to make sure, are you looking at DRV10970 or DRV10974?

    Sincerely,
    Sanmesh U.
  • 0 in reply to Sanmesh Udhayakumar
    TI__Intellectual 2900 points

    Hi Sanmesh,

    I am looking at the DRV10970.

    Please also help to check the resolution and the error of the speed commend using the PWM.

    Lacey

    Thanks a lot!

  • 0 in reply to Lacey Lin
    TI__Expert 6065 points
    Resolution of the pwm speed command is 0.4%.

    Please let me know if this answered your question. If it has, please click the resolved button
  • 0 in reply to Sanmesh Udhayakumar
    TI__Intellectual 2900 points
    Hi Sanmesh,
    Thanks so much for your feedback!
    Can you also help to check the max error for the PWM commend.
    As a example, if the input PWM duty cycle is set to 50%, what's the max error for the actual speed?
    Lacey
    Thanks a lot!
  • 0 in reply to Lacey Lin
    TI__Expert 6065 points
    1) PWM is 8 bits resolution for duty. So resolution of speed cmd = 100%/2^8 = about 0.4%. We expect around 1 bit or error so around 0.4% error +-. This is the speed cmd resolution.
    2) What DRV10970 controls is the peak amplitude of the voltage applied. It doesnt control exact speed. Actual Speed may vary with varying load torque. Yuo can set up a speed loop by using FG pin as speed feedback and adjusting the pwm duty. Reference materials is below:
    a) “Utilizing the DRV10 Frequency Generator for Closed-Loop Speed Control” app note. (www.ti.com/.../litabsmultiplefilelist.tsp
    Description: Explains how to use the FG pin on the DRV10x devices to do speed control. Uses the DRV10866 for this example, but fg discussion also relatable to DRV10970. Look at particularly section “2.5 Pseudo code”.

    Please let me know if this answered your question. If it has, please click the resolved button